Thin plastic filaments made of polypropylene or some other suitable, nontoxic material are used to support certain types of intraocular lenses within the eye after it has been implanted to replace the natural lens of the eye that has been removed to correct some vision impairment, for example cataracts. Such support filaments are used on lenses like that shown in U.S. Pat. No. 4,159,546 (the Shearing patent). The properties and use of such support filaments are thoroughly described in the Shearing patent which is incorporated by reference in this patent application.
It will be appreciated that all the surfaces of the intraocular lens should be smooth and rounded to avoid damaging the eye during intraocular lens implant surgery or during use of the lens after implantation. It is particularly important that the free end of the support loops shown in the Shearing patent be as round and smooth as possible to avoid damaging the interior anatomy of the eye.
In the past, various loop finishing processes have been used to remove sharp corners that result from cutting and forming the loops during the manufacturing process. Thermal forming and abrasive tumbling have been used to provide this smoothing. Although these methods remove sharp edges and provide an acceptable degree of rounding to the ends of the loops, further improvement to form an ideal hemispherical end would be desirable.
Other methods for smoothing and rounding the terminal portion of an open loop are shown in U.S. Pat. No. 4,242,760 where a knob is fixed to the end of the open loop to prevent damage to human tissue within the eye. Similar rounded ends for support loops are shown in U.S. Pat. Nos. 4,244,060 and 4,366,582.
It would be desirable to have an improved apparatus and method for forming round ends on small plastic filaments.